As shown in FIG. 1A, a light-emitting path of conventional light-emitting elements, such as the light-emitting diode (LED) 15, is perpendicular to a light-emitting surface of the light-emitting elements, and the energy distribution thereof is Lambert's type. The conventional light-emitting elements are usually applied to traffic signals, illuminators or other guide signs. However, as shown in FIG. 1B, when multiple LEDs 15 and 15′ are arranged together to mix optical properties, such as mixing light intensity or light color. The mixing effect can be obtained at a given distance away from the light-emitting surface. An invalid distance D1 is the given distance where the mixing effect does not appear. If the light distribution pattern of the emitted light can be flattened, the invalid distance D1 will be shortened obviously.
As shown in FIG. 2, a conventional side-emitting light-emitting diode of U.S. Pat. No. 6,598,998 B2, entitled “Side Emitting Light Emitting Device” issued to Lumileds Co., discloses a side-emitting light-emitting diode having a special packaging lens. Such kind of side-emitting light-emitting diode has multiple refractive surfaces 14, which have an oblique angle with respect to an optical axis L of the packaging lens. Although most light energy passes through the refractive surfaces 14 which the side surface of the packaging lens and is emitted therefrom, a small portion of light energy (less than 10%) still is emitted from the top of the packaging lens (i.e. along the direction of the optical axis L). Therefore, a light-shield sheet is stuck onto the top of the packaging lens of this kind of side-emitting light-emitting diode to reflect back the light proceeding upward.
Refer to FIG. 3. U.S. Pat. No. 6,679,621 B2, entitled “Side Emitting LED and lens”, issued to the abovementioned Lumileds Co. discloses another packaging lens as shown in FIG. 3. The packaging lens comprises an incident surface 10, a reflective surface 11, a first refractive surface 12 and a second refractive surface 13. After a light from a light source enters into the packaging structure through the incident surface 10, the light proceeds primarily along two paths P1, P2 and is emitted out thereby. The light enters into the packaging structure through the incident surface 10 to be reflected by the reflective surface 11 via total internal reflection then to penetrate the first refractive surface 12 along the path P1. The light enters into the packaging structure through the incident surface 10 and then to penetrate the second refractive surface 13 directly along the path P2. However, the abovementioned conventional technology has the following problems.
First, when the light reflected by the reflective surface 11 is not incident the first refractive surface 12 in an incident angle with a right angle, and it results in the energy loss; further, when the incident angle is too great it brings about a total reflection.
Second, a portion of the light reflected by the first refractive 12 penetrates the reflective surface 11 and forms light spots or light halos on LED. This results in the light energy loss and an undesired light distribution pattern and needs a shielding sheet or a diffusive sheet.
Third, an intersection formed by the reflective face 11 and the first refractive face 12 is an acute angle to result in a fragile structure of the packaging lens.